A coalition of pressure groups will on Monday unveil a new campaign against three controversial sponsors of the London Olympics, accusing them of using the Games to "greenwash" unethical corporate activities.

With the growing prospect of protests at the Games by groups seeking to highlight the activities of its corporate backers and others planning to use it as a broader canvas to protest against capitalism, the Greenwash Gold campaign marks a new level of co-ordination.

The coalition – bringing together protest groups campaigning against Olympic sponsors Dow Chemical, BP and Rio Tinto – is chaired by Meredith Alexander, who quit as a commissioner of the London 2012 sustainability watchdog over Dow's $100m (£63m) deal with the International Olympic Committee and its agreement with London organisers to fund the £7m wrap that will surround the stadium.

The three companies have been made the subject of short animated films, with members of the public invited to vote online for the "worst corporate sponsor of the Olympics". The company that tops the poll will receive the "Greenwash gold medal" from organisers, who claim that the involvement of the companies is putting the image of the London Games at risk.

"The modern Olympics was founded here in the UK to promote peace and understanding between the peoples of the world. The Olympic values are all about celebrating our common humanity," said Alexander.

"But the Olympics is also big business. There is an expensive machine behind the Games that is funded by corporate sponsors. Sadly when these sponsors are selected, money talks much more loudly than values."

She said the strength of the UK's campaigning sector would help shine a light on the issue and put pressure on the IOC to change the way it selects sponsors.

"The fact that it's difficult to know where to draw the line doesn't mean a line shouldn't be drawn. What the IOC is doing at the moment is putting its hands up and giving up. Given the value of the Olympic brand to these companies, I think that is unacceptable," said Alexander.

She said that while London organisers had made some positive moves in trying to encourage ethical suppliers, the IOC had been reluctant to use its power to force companies to raise their standards before signing up as sponsors.

The IOC's so-called TOP sponsors pay at least $100m each for 10-year contracts, while Tier One sponsors for the London Games alone have paid around £40m each. London 2012 organisers have raised £700m from domestic sponsors towards the £2bn cost of staging the Games.

Dow's sponsorship has proved controversial with campaigners, who claim it has outstanding liabilities relating to the 1984 Bhopal disaster in India, which killed up to 20,000 people and injured tens of thousands more.

The company denies the claims, arguing it was neither the owner nor operator of Union Carbide, the plant's owner at the time of the disaster, and that the company had divested of its Indian assets by the time Dow acquired it in 1999.

But protesters, led by a group of MPs headed by Barry Gardiner and including London mayoral candidate Ken Livingstone, also have a long list of other grievances. Following a demonstration during a recent IOC inspection visit, London 2012 chairman Lord Coe agreed to meet with protesters.

BP has been targeted by protest groups including the UK Tar Sands Network, which believe that the extraction of polluting tar sands and the damage caused by the Deepwater Horizon disaster make it "one of the least sustainable companies on earth".

BP is the lead sponsor of the Cultural Olympiad, has organised a Young Leaders mentoring programme and is encouraging those travelling to the Games to offset their carbon in campaigns featuring the likes of Jessica Ennis.

But Jess Worth, from the UK Tar Sands Network, said: "BP has bought itself the prestigious title of London 2012 sustainability partner. But this is dangerous greenwash. BP is one of the least sustainable companies on earth, responsible for the Deepwater Horizon disaster and the extraction of highly-polluting tar sands. Its entire business is geared towards keeping the world addicted to fossil fuels and driving us towards uncontrollable climate change."

Also present at a launch event will be representatives from some of the communities that claim to have been affected by the activities of the three multinational companies.

They include a survivor of the Bhopal disaster, an organiser from an indigenous communities in Canada fighting BP's tar sands operation, and a woman from Utah who campaigns against alleged air pollution caused by one of the mines from which Rio Tinto is providing the metal for Olympic medals.

Cherise Udell, the founder of Utah Moms for Clean Air, said: "I was delighted to learn that the 2012 Olympic committee was aiming for the greenest Olympics ever. Then I heard that Rio Tinto metal from our controversial Utah mine would be used to make the medals. In Utah, Rio Tinto are the number one emitter of toxins known to cause harm to human health."

All three companies have defended their ethical record and their involvement in the Games.

In the wake of a stunt last week that fooled some media outlets into believing BP had been dropped as a sponsor, Mike Sharrock, BP's partnership director for London 2012, said: "What we'll try and do is just focus on what we're doing. We're confident our contribution is a positive one. What we have tried to do is make sure that everything we're doing is credible and authentic."

The Metropolitan police and Paul Deighton, chief executive of the London Organising Committee for the Olympic and Paralympic Games, have said that peaceful protest would be facilitated but that disruption will be clamped down on.

"I have a simple philosophical view about this. People have the right to protest and express their point of view. I think that's wonderful," said Deighton. "When it gets to the point where their clamour for recognition stifles the joy of millions, we all have to look at it and deal with it."